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Guyton and Hall Textbook of Medical Physiology, 13th Edition

John E Hall, PhD

978-1-4557-7005-2

Unlike other physiology textbooks, this

clear and comprehensive guide has a

consistent, single-author voice and focuses

on the content most relevant to clinicaland pre-clinical students The detailedbut lucid text is complemented by didactic illustrations that summarize key concepts

in physiology and pathophysiology

Pocket Companion to Guyton and Hall Textbook of Medical Physiology, 13th Edition

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GUYTON AND HALL

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Pocket Companion

to Guyton and Hall Textbook

of Medical Physiology Thirteenth Edition

John E Hall, PhD

Arthur C Guyton Professor and ChairDepartment of Physiology and BiophysicsDirector of the Mississippi Center for Obesity Research

University of Mississippi Medical Center

Jackson, Mississippi

POCKET COMPANION TO GUYTON AND

HALL TEXTBOOK OF MEDICAL PHYSIOLOGY,

THIRTEENTH EDITION

Copyright © 2016 by Elsevier, Inc All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher Details on how to seek permission, further information about the Pub- lisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under right by the Publisher (other than as may be noted herein).

copy-Notices

Knowledge and best practice in this field are constantly changing As new search and experience broaden our understanding, changes in research meth- ods, professional practices, or medical treatment may become necessary Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds,

re-or experiments described herein In using such infre-ormation re-or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of admin- istration, and contraindications It is the responsibility of practitioners, relying

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To the fullest extent of the law, neither the Publisher nor the authors, tributors, or editors, assume any liability for any injury and/or damage to per- sons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

con-Previous editions copyrighted 2012, 2006, 2001, 1998 by Saunders, an imprint of Elsevier, Inc.

Library of Congress Cataloging-in-Publication Data

Hall, John E (John Edward), 1946- , author.

Pocket companion to Guyton and Hall textbook of medical physiology / John E Hall Thirteenth edition.

p ; cm.

Complemented by: Guyton and Hall textbook of medical physiology / John E Hall Thirteenth edition [2016].

Includes index.

ISBN 978-1-4557-7006-9 (paperback : alk paper)

I Hall, John E (John Edward), 1946- Guyton and Hall textbook of medical physiology Complemented by (expression): II Title.

[DNLM: 1 Physiological Phenomena QT 104]

QP35

Senior Content Strategist: Elyse O’Grady

Senior Content Development Manager: Rebecca Gruliow

Publishing Services Manager: Patricia Tannian

Senior Project Manager: Carrie Stetz

Design Direction: Julia Dummitt

Printed in The United States of America

Last digit is the print number: 9 8 7 6 5 4 3 2 1

Philadelphia, PA 19103-2899 ISBN: 978-1-4557-7006-9

Contributors

Thomas H Adair, PhD

Professor of Physiology and Biophysics

University of Mississippi Medical Center

Arthur C Guyton Professor and Chair

Department of Physiology and Biophysics

Director, Mississippi Center for Obesity ResearchUniversity of Mississippi Medical Center

Jackson, Mississippi

Introduction to Physiology: The Cell and General Physiology (Chapters 1–3)

The Circulation (Chapters 14–19)

The Body Fluids and Kidneys (Chapters 25–32) Blood Cells, Immunity, and Blood Coagulation (Chapters 33–37)

The Nervous System: C Motor and Integrative Neurophysiology (Chapters 61–62)

Metabolism and Temperature Regulation

The Heart (Chapters 9–13)

The Circulation (Chapters 20–24)

Preface

Human physiology is the discipline that links the basic sciences with clinical medicine It is integrative and encompasses the study of molecules and subcellular components, cells, tissues, and organ systems, as well

as the feedback systems that coordinate these nents of the body and permit us to function as living beings Because human physiology is a rapidly expand-ing discipline and covers a broad scope, the vast amount

compo-of information that is applicable to the practice compo-of cine can be overwhelming Therefore, one of our major

medi-goals for writing this Pocket Companion was to distill

this enormous amount of information into a book that would be small enough to be carried in a coat pocket and used often but still contain most of the basic physi-ological principles necessary for the study of medicine

The Pocket Companion was designed to accompany

Guyton and Hall Textbook of Medical Physiology, 13th

Edition, not substitute for it It is intended to serve as a concise overview of the most important facts and con-cepts from the parent text, presented in a manner that facilitates rapid comprehension of basic physiological principles Some of the most important features of the

Pocket Companion are as follows:

• It was designed to serve as a guide for students who wish to review a large volume of material from the parent text rapidly and efficiently The headings of the sections state succinctly the primary concepts

in the accompanying paragraphs Thus, the student can quickly review many of the main concepts in the textbook by first studying the paragraph headings

• The table of contents matches that of the parent text, and each topic has been cross-referenced with spe-cific page numbers from the parent text The pocket companion has been updated in parallel with the

Textbook of Medical Physiology, 13th edition.

• The size of the book has been restricted so it can fit conveniently in a coat pocket as an immediate source of information

Although the Pocket Companion contains the most

important facts necessary for studying physiology, it does not contain the details that enrich the physiological concepts or the clinical examples of abnormal physiol-ogy that are contained in the parent book We therefore

recommend that the Pocket Companion be used in junction with the Textbook of Medical Physiology, 13th

con-Edition

I am grateful to each of the contributors for their careful work on this book Contributing authors were selected for their knowledge of physiology and their ability to present information effectively to students

We also greatly appreciate the excellent work of Rebecca Gruliow, Elyse O’Grady, Carrie Stetz, and the entire Elsevier team for continued editorial and production excellence

We have strived to make this book as accurate as possible and hope that it will be valuable for your study

of physiology Your comments and suggestions for ways

to improve the Pocket Companion are always greatly

appreciated

John E Hall, PhD Jackson, Mississippi

CHAPTER 12

Electrocardiographic Interpretation of Cardiac Muscle and Coronary Blood Flow Abnormalities: Vectorial Analysis, 79

CHAPTER 22

Cardiac Failure, 154

CHAPTER 23

Heart Valves and Heart Sounds; Valvular and

Congenital Heart Defects, 160

Urine Concentration and Dilution; Regulation

of Extracellular Fluid Osmolarity and Sodium

Concentration, 209

CHAPTER 30

Renal Regulation of Potassium, Calcium, Phosphate, and Magnesium; Integration of Renal Mechanisms for Control of Blood Volume and Extracellular Fluid Volume, 218

Organization of the Nervous System, Basic Functions

of Synapses, and Neurotransmitters, 333

CHAPTER 47

Sensory Receptors, Neuronal Circuits for Processing Information, 340

CHAPTER 48

Somatic Sensations: I General Organization,

the Tactile and Position Senses, 345

CHAPTER 57

Contributions of the Cerebellum and Basal Ganglia

to Overall Motor Control, 410

Parathyroid Hormone, Calcitonin, Calcium

and Phosphate Metabolism, Vitamin D, Bone, and Teeth, 579

CHAPTER 81

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland), 588

UNIT I

Introduction to Physiology: The Cell

and General Physiology

1 Functional Organization of the Human Body and Control of the “Internal Environment,” 3

2 The Cell and Its Functions, 9

3 Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction, 19

Physiology is the science that seeks to understand the

function of living organisms and their parts In human

physiology, we are concerned with the characteristics of the human body that allow us to sense our environment, move about, think and communicate, reproduce, and perform all of the functions that enable us to survive and thrive as living beings

Human physiology is a broad subject that attempts

to explain the specific characteristics and nisms of the human body that make it a living being The subject includes the functions of molecules and subcellular components; tissues; organs; organ sys-tems, such as the cardiovascular system; and the interaction and communication among these compo-nents A distinguishing feature of physiology is that

mecha-it seeks to integrate the functions of all of the parts

of the body to understand the function of the entire human body Life in the human being relies on this total function, which is considerably more complex than the sum of the functions of the individual cells, tissues, and organs

Cells Are the Living Units of the Body Each organ is an aggregate of many cells held together by intercellular supporting structures The entire body contains about 100 trillion cells, each of which is adapted

to perform special functions These individual cell functions are coordinated by multiple regulatory systems operating in cells, tissues, organs, and organ systems

Although the many cells of the body differ from each other in their special functions, all of them have certain basic characteristics For example, (1) oxygen combines with breakdown products of fat, carbohy-drates, or protein to release energy that is required for function of the cells; (2) most cells have the abil-ity to reproduce, and whenever cells are destroyed, the remaining cells often regenerate new cells until the appropriate number is restored; and (3) cells are bathed in extracellular fluid, the constituents of which are precisely controlled

CHAPTER 1

Functional Organization of the Human Body and Control of the “Internal

Environment”

Introduction to Physiology: The Cell and General Physiology

per-condition called homeostasis Much of our discussion

of physiology focuses on mechanisms by which the cells, tissues, and organs contribute to homeostasis

Extracellular Fluid Transport and Mixing

System—The Blood Circulatory System

Extracellular fluid is transported throughout the body

in two stages The first stage is movement of blood

throughout the circulatory system, and the second

stage is movement of fluid between the blood laries and cells The circulatory system keeps the flu-ids of the internal environment continuously mixed

capil-by pumping blood through the vascular system As blood passes through the capillaries, a large portion

of its fluid diffuses back and forth into the tial fluid that lies between the cells, allowing continu-ous exchange of substances between the cells and the interstitial fluid and between the interstitial fluid and the blood

intersti-Origin of Nutrients in the Extracellular Fluid

• The respiratory system provides oxygen for the body

and removes carbon dioxide

• The gastrointestinal system digests food and

facili-tates absorption of various nutrients, including bohydrates, fatty acids, and amino acids, into the extracellular fluid

• The liver changes the chemical composition of

many of the absorbed substances to more able forms, and other tissues of the body (e.g., fat cells, kidneys, endocrine glands) help modify the absorbed substances or store them until they are needed

• The musculoskeletal system consists of skeletal

mus-cles, bones, tendons, joints, cartilage, and ligaments Without this system, the body could not move to the appropriate place to obtain the foods required for nutrition This system also protects internal organs and supports the body

Functional Organization of the Human Body and Control of the

“Internal Environment” 5Removal of Metabolic End Products (p 5)

• The respiratory system not only provides oxygen to

the extracellular fluid but also removes carbon ide, which is produced by the cells, released from the blood into the alveoli, and then released to the exter-nal environment

• The kidneys excrete most of the waste products

other than carbon dioxide The kidneys play a jor role in regulating extracellular fluid composition

ma-by controlling excretion of salts, water, and waste products of the chemical reactions of the cells By controlling body fluid volumes and compositions, the kidneys also regulate blood volume and blood pressure

• The liver eliminates certain waste products

pro-duced in the body, as well as toxic substances that are ingested

Regulation of Body Functions

• The nervous system directs the activity of the

muscular system, thereby providing locomotion

It also controls the function of many internal gans through the autonomic nervous system, and

or-it allows us to sense our external and internal vironment and to be intelligent beings so we can obtain the most advantageous conditions for sur-vival

• The hormone systems control many metabolic

func-tions of the cells, such as growth, rate of metabolism, and special activities associated with reproduction Hormones are secreted into the bloodstream and are carried to tissues throughout the body to help regu-late cell function

Protection of the Body

• The immune system provides the body with a defense

mechanism that protects against foreign invaders, such as bacteria and viruses, to which the body is exposed daily

• The integumentary system, which is composed

mainly of skin, provides protection against injury and defense against foreign invaders, as well as protection of underlying tissues against dehydra-tion The skin also serves to regulate body temper-ature

Introduction to Physiology: The Cell and General Physiology

Reproduction

The reproductive system provides for formation of new

beings like ourselves Even this function can be ered a homeostatic function because it generates new bodies in which trillions of additional cells can exist in a well-regulated internal environment

consid-CONTROL SYSTEMS OF THE BODY (p 6)

The human body has thousands of control systems that are essential for homeostasis For example, genetic systems operate in all cells to control intracellular and extracellular functions Other control systems operate within the organs or throughout the entire body to con-trol interactions among the organs

Regulation of oxygen and carbon dioxide tions in the extracellular fluid is a good example of multi-

concentra-ple control systems that operate together In this instance, the respiratory system operates in association with the nervous system When carbon dioxide concentration in the blood increases above normal, the respiratory center is excited, causing the person to breathe rapidly and deeply This breathing increases the expiration of carbon dioxide and therefore removes it from the blood and the extracel-lular fluid until the concentration returns to normal

Normal Ranges of Important Extracellular

Fluid Constituents

Table 1–1 shows some important constituents of cellular fluid along with their normal values, normal ranges, and maximum limits that can be endured for short periods without the occurrence of death Note the narrowness of the ranges; levels outside these ranges are usually the cause or the result of illnesses

extra-Characteristics of Control Systems

Most Control Systems of the Body Operate by Negative Feedback For regulation of carbon dioxide concentration, as discussed, a high concentration of carbon dioxide in the extracellular fluid increases pulmonary ventilation, which decreases carbon dioxide concentration, moving it toward normal levels This

mechanism is an example of negative feedback; that is,

any stimulus that attempts to change the carbon dioxide concentration is counteracted by a response that is

negative to the initiating stimulus.

Functional Organization of the Human Body and Control of the

“Internal Environment” 7

The degree of effectiveness with which a control system maintains constant conditions is determined by

the gain of the negative feedback The gain is calculated

according to the following formula:

Gain = Correction/Error

Some control systems, such as those that regulate body temperature, have feedback gains as high as −33, which simply means that the degree of correction is 33 times greater than the remaining error

Feed-Forward Control Systems Anticipate Changes

Because of the many interconnections between control systems, the total control of a particular body function may be more complex than can be accounted for

by simple negative feedback For example, some movements of the body occur so rapidly that there is not sufficient time for nerve signals to travel from some

of the peripheral body parts to the brain and then back

to the periphery in time to control the movements Therefore, the brain uses feed-forward control to cause the required muscle contractions Sensory nerve signals from the moving parts inform the brain in retrospect

of whether the appropriate movement, as envisaged by

Table 1–1 Some Important Constituents and Physical

Characteristics of the Extracellular Fluid, Normal Range of Control, and Approximate Nonlethal Limits for Short Periods

Average Normal Values Normal Ranges

Approximate Nonlethal LimitsOxygen (venous) mm Hg 40 35–45 10–1000Carbon dioxide

(venous)

Sodium ion mmol/L 142 138–146 115–175Potassium ion mmol/L 4.2 3.8–5.0 1.5–9.0Calcium ion mmol/L 1.2 1.0–1.4 0.5–2.0Chloride ion mmol/L 106 103–112 70–130Bicarbonate ion mmol/L 24 22–29 8–45

Body temperature °F (°C) 98.4

(37.0)

98–98.8 (37.0)

65–110 (18.3–43.3)

Introduction to Physiology: The Cell and General Physiology

the brain, has been performed correctly If it has not, the brain corrects the feed-forward signals it sends to the muscles the next time the movement is required This

process is also called adaptive control, which is, in a

sense, delayed negative feedback

Positive Feedback Can Sometimes Cause Vicious Cycles and Death, and Other Times It Can Be Useful A system that exhibits positive feedback responds to a perturbation with changes that amplify the perturbation and therefore leads to instability rather than stability For example, severe hemorrhage may lower blood pressure to such

a low level that blood flow to the heart is insufficient

to maintain normal cardiac pumping; as a result, blood pressure falls even lower, further diminishing blood flow to the heart and causing still more weakness of the heart Each cycle of this feedback leads to more of the

same, which is a positive feedback or a vicious cycle.

In some cases the body uses positive feedback to its advantage An example is the generation of nerve sig-nals When the nerve fiber membrane is stimulated, the slight leakage of sodium ions into the cell causes open-ing of more channels, more sodium entry, more change

in membrane potential, and so forth Therefore, a slight leak of sodium into the cell becomes an explosion of sodium entering the interior of the nerve fiber, which creates the nerve action potential

SUMMARY—AUTOMATICITY OF THE BODY (p 10)

The body is a social order of about 100 trillion cells

orga-nized into various functional structures, the largest of

which are called organs Each functional structure, or

organ, helps maintain a constant internal ment As long as homeostasis is maintained, the cells

environ-of the body continue to live and function properly Thus, each cell benefits from homeostasis and, in turn, each cell contributes its share toward maintenance of homeostasis This reciprocal interplay provides con-

tinuous automaticity of the body until one or more

functional systems lose their ability to contribute their share of function When this loss happens, all the cells

of the body suffer Extreme dysfunction leads to death, whereas moderate dysfunction leads to sickness

ORGANIZATION OF THE CELL (p 11)

Figure 2–1 shows a typical cell, including the nucleus and cytoplasm, which are separated by the nuclear

membrane The cytoplasm is separated from interstitial fluid by a cell membrane that surrounds the cell The

substances that make up the cell are collectively called

protoplasm, which is composed mainly of the following:

• Water constitutes 70 percent to 85 percent of most

cells

• Ions/electrolytes provide inorganic chemicals for

cel-lular reactions Some of the most important ions in

the cell are potassium, magnesium, phosphate,

sul-fate, bicarbonate, and small quantities of sodium, chloride, and calcium.

• Proteins normally constitute 10 to 20 percent of the cell mass They can be divided into two types: struc-

tural proteins and globular (functional) proteins,

which are mainly enzymes.

• Lipids constitute about 2 percent of the total cell

mass Among the most important lipids in the cells

are phospholipids, cholesterol, triglycerides, and

neu-tral fats In adipocytes (fat cells), triglycerides

ac-count for as much as 95 percent of the cell mass and represent the body’s main energy storehouse

• Carbohydrates play a major role in nutrition of the

cell Most human cells do not store large amounts of carbohydrates, which usually average about 1 percent

of the total cell mass but may be as high as 3 percent

in muscle cells and 6 percent in liver cells The small amount of carbohydrates in the cells is usually stored in

the form of glycogen, an insoluble polymer of glucose.

PHYSICAL STRUCTURE OF THE CELL (p 12)

The cell (Figure 2–1) is not merely a bag of fluid and chemicals; it also contains highly organized physi-

cal structures called organelles Some of the principal organelles of the cell are the cell membrane, nuclear

membrane, endoplasmic reticulum (ER), Golgi tus, mitochondria, lysosomes, and centrioles.

appara-The Cell and Its Organelles Are Surrounded by Membranes Composed of Lipids and Proteins The membranes that surround the cell and its organelles

CHAPTER 2

The Cell and Its Functions

Introduction to Physiology: The Cell and General Physiology

include the cell membrane, nuclear membrane, and

membranes of the ER, mitochondria, lysosomes, and Golgi apparatus They provide barriers that prevent

free movement of water and water-soluble substances from one cell compartment to another Proteins in the membrane often penetrate the membrane, providing pathways (channels) to allow movement of specific substances through the membranes

The Cell Membrane Is a Lipid Bilayer With Inserted Proteins The lipid bilayer is composed almost entirely

of phospholipids, sphingolipids, and cholesterol

Phos-pholipids are the most abundant of the cell lipids

and have a water-soluble (hydrophilic) portion and

a portion that is soluble only in fats (hydrophobic)

The hydrophobic portions of the phospholipids face each other, whereas the hydrophilic parts face the two surfaces of the membrane in contact with the surrounding interstitial fluid and the cell cytoplasm.This lipid bilayer membrane is highly permeable to lipid-soluble substances, such as oxygen, carbon diox-ide, and alcohol, but it acts as a major barrier to water-soluble substances, such as ions and glucose Floating in

the lipid bilayer are proteins, most of which are

glyco-proteins (glyco-proteins combined with carbohydrates).

Nucleolus

Cell membrane

reticulum

Smooth (agranular) endoplasmic reticulum

Ribosomes Glycogen

Golgi apparatus

Microfilaments Chromosomes and DNA

Figure 2–1 Reconstruction of a typical cell, showing the internal ganelles in the cytoplasm and nucleus

or-The Cell and Its Functions 11

There are two types of membrane protein: the

inte-gral proteins, which protrude through the membrane,

and the peripheral proteins, which are attached to the

inner surface of the membrane and do not penetrate

Many of the integral proteins provide structural

chan-nels (pores) through which water-soluble substances,

especially ions, can diffuse Other integral proteins

act as carrier proteins for the transport of substances,

sometimes against their gradients for diffusion

Integral proteins can also serve as receptors for

sub-stances, such as peptide hormones, that do not easily penetrate the cell membrane

The peripheral proteins are normally attached to one

of the integral proteins and usually function as enzymes

that catalyze chemical reactions of the cell

The membrane carbohydrates occur mainly in

com-bination with proteins and lipids in the form of

glyco-proteins and glycolipids The “glyco” portions of these

molecules usually protrude to the outside of the cell

Many other carbohydrate compounds, called

proteogly-cans, which are mainly carbohydrate substances bound

together by small protein cores, are loosely attached

to the outer surface; thus, the entire outer surface of the cell often has a loose carbohydrate coat called the

glycocalyx.

The carbohydrates on the outer surface of the cell have multiple functions: (1) they are often negatively charged and therefore repel other molecules that are negatively charged; (2) the glycocalyx of cells may attach

to other cells (thus the cells attach to each other); (3)

some of the carbohydrates act as receptors for binding

hormones; and (4) some carbohydrate moieties enter into immune reactions, as discussed in Chapter 35

The Endoplasmic Reticulum Synthesizes Multiple Substances in the Cell A large network of tubules

and vesicles, called the endoplasmic reticulum (ER),

penetrates almost all parts of the cytoplasm The ER membrane provides an extensive surface area for the manufacture of many substances used inside the cells and released from some cells They include proteins, carbohydrates, lipids, and other structures such as lysosomes, peroxisomes, and secretory granules.Lipids are made within the ER wall For the synthesis

of proteins, ribosomes attach to the outer surface of the

granular ER These ribosomes function in association

with messenger RNA to synthesize many proteins that

then enter the Golgi apparatus, where the molecules are further modified before they are released or used in the cell Part of the ER has no attached ribosomes and is

called the agranular, or smooth, ER The agranular ER

Introduction to Physiology: The Cell and General Physiology

functions for the synthesis of lipid substances and for other processes of the cells promoted by intrareticular enzymes

The Golgi Apparatus Functions in Association With the ER The Golgi apparatus has membranes similar to those of the agranular ER, is prominent in secretory cells, and is located on the side of the cell from which

the secretory substances are extruded Small transport

vesicles, also called ER vesicles, continually pinch off

from the ER and then fuse with the Golgi apparatus

In this way, substances entrapped in the ER vesicles are transported from the ER to the Golgi apparatus The substances are then processed in the Golgi apparatus

to form lysosomes, secretory vesicles, and other cytoplasmic components

Lysosomes Provide an Intracellular Digestive System

Lysosomes, which are found in great numbers in many cells, are small spherical vesicles surrounded by

a membrane that contains digestive enzymes These enzymes allow lysosomes to break down intracellular substances in structures, especially damaged cell structures, food particles that have been ingested by the cell, and unwanted materials such as bacteria

The membranes surrounding the lysosomes usually prevent the enclosed enzymes from coming in contact with other substances in the cell and therefore prevent their digestive action When these membranes are dam-aged, the enzymes are released and split the organic substances with which they come in contact into highly diffusible substances such as amino acids and glucose

Mitochondria Release Energy in the Cell An adequate supply of energy must be available to fuel the chemical reactions of the cell This energy is provided mainly by the chemical reaction of oxygen with the three types

of foods: glucose derived from carbohydrates, fatty acid derived from fats, and amino acids derived from proteins After entering the cell, foods are split into smaller molecules that, in turn, enter the mitochondria, where other enzymes remove carbon dioxide and

hydrogen ions in a process called the citric acid cycle

An oxidative enzyme system, which is also in the mitochondria, causes progressive oxidation of hydrogen atoms The end products of mitochondria reactions are water and carbon dioxide The energy liberated is used by mitochondria to synthesize another substance,

adenosine triphosphate (ATP), a highly reactive

chemical that can diffuse throughout the cell to release its energy whenever it is needed for the performance of cell functions

The Cell and Its Functions 13

Mitochondria are also self-replicative, which means that one mitochondrion can form a second one, a third one, and so on whenever there is a need in the cell for increased amounts of ATP

There Are Many Cytoplasmic Structures and Organelles

Hundreds of types of cells are found in the body, and each has a special structure Some cells, for example, are

rigid and have large numbers of filamentous or tubular

structures, which are composed of fibrillar proteins A

major function of these tubular structures is to act as

a cytoskeleton, providing rigid physical structures for

certain parts of cells Some of the tubular structures,

called microtubules, can transport substances from one

area of the cell to another

One of the important functions of many cells is to secrete special substances, such as digestive enzymes Almost all of the substances are formed by the ER-Golgi apparatus system and are released into the cyto-

plasm inside storage vesicles called secretory vesicles

After a period of storage in the cell, they are expelled through the cell membrane to be used elsewhere in the body

The Nucleus Is the Control Center of the Cell and

Contains Large Amounts of DNA, Also Called Genes (p 17)

Genes determine the characteristics of the proteins

of the cell, including the enzymes of the cytoplasm They also control reproduction Genes first reproduce

themselves through a process of mitosis in which two

daughter cells are formed, each of which receives one of the two sets of genes

The nuclear membrane, also called the nuclear

enve-lope, separates the nucleus from the cytoplasm This

structure is composed of two membranes; the outer membrane is continuous with the ER, and the space between the two nuclear membranes is also continuous with the compartment inside the ER Both layers of the

membrane are penetrated by several thousand nuclear

pores, which are almost 100 nanometers in diameter.

The nuclei in most cells contain one or more

structures called nucleoli, which, unlike many of the

organelles, do not have a surrounding membrane The nucleoli contain large amounts of RNA and proteins

of the type found in ribosomes A nucleolus becomes enlarged when the cell is actively synthesizing proteins Ribosomal RNA is stored in the nucleolus and trans-ported through the nuclear membrane pores to the cytoplasm, where it is used to produce mature ribo-somes, which play an important role in the formation

of proteins

Introduction to Physiology: The Cell and General Physiology

FUNCTIONAL SYSTEMS OF THE CELL (p 19)

Ingestion by the Cell—Endocytosis

The cell obtains nutrients and other substances from the surrounding fluid through the cell membrane via

diffusion and active transport Very large particles enter

the cell via endocytosis, the principal forms of which are

pinocytosis and phagocytosis.

• Pinocytosis is the ingestion of small globules of

ex-tracellular fluid, forming minute vesicles in the cell cytoplasm This process is the only method by which

large molecules, such as proteins, can enter the cells These molecules usually attach to specialized recep-tors on the outer surface of the membrane that are

concentrated in small pits called coated pits On the

inside of the cell membrane underneath these pits is

a latticework of a fibrillar protein called clathrin and

a contractile filament of actin and myosin After the

protein molecules bind with the receptors, the brane invaginates and contractile proteins surround the pit, causing its borders to close over the attached

mem-proteins and form a pinocytotic vesicle.

• Phagocytosis is the ingestion of large particles, such

as bacteria, cells, and portions of degenerating tissue

This ingestion occurs much in the same way as cytosis except that it involves large particles instead

pino-of molecules Only certain cells have the ability to

perform phagocytosis, notably tissue macrophages and some white blood cells Phagocytosis is initiated

when proteins or large polysaccharides on the face of the particle bind with receptors on the sur-face of the phagocyte In the case of bacteria, these usually are attached to specific antibodies, and the antibodies in turn attach to the phagocyte receptors, dragging the bacteria along with them This inter-

sur-mediation of antibodies is called opsonization and is

discussed further in Chapters 34 and 35

Pinocytic and Phagocytic Foreign Substances Are Digested in the Cell by the Lysosomes Almost as soon

as pinocytic or phagocytic vesicles appear inside a cell, lysosomes become attached to the vesicles and empty their digestive enzymes into the vesicle Thus, a

digestive vesicle is formed in which the enzymes begin

hydrolyzing the proteins, carbohydrates, lipids, and other substances in the vesicle The products of digestion are small molecules of amino acids, glucose, phosphate, and so on that can diffuse through the membrane of the vesicle into the cytoplasm The undigested substances,

called the residual body, are excreted through the

The Cell and Its Functions 15

cell membrane via the process of exocytosis, which is

basically the opposite of endocytosis

Synthesis of Cellular Structures by ER and Golgi Apparatus (p 20)

The Synthesis of Most Cell Structures Begins in the ER

Many of the products formed in the ER are then passed onto the Golgi apparatus, where they are further processed before release into the cytoplasm

The granular ER, characterized by large numbers of

ribosomes attached to the outer surface, is the site of protein formation Ribosomes synthesize the proteins and extrude many of them through the wall of the ER

to the interior of the endoplasmic vesicles and tubules,

called the endoplasmic matrix.

When proteins enter the ER, enzymes in the ER wall cause rapid changes, including congregation of carbo-

hydrates to form glycoproteins In addition, the proteins

are often cross-linked, folded, and shortened to form more compact molecules

The ER also synthesizes lipids, especially lipid and cholesterol, which are incorporated into the

phospho-lipid bilayer of the ER Small ER vesicles, or transport

vesicles, continually break off from the smooth

reticu-lum Most of these vesicles migrate rapidly to the Golgi apparatus

The Golgi Apparatus Processes Substances Formed in the ER As substances are formed in the ER, especially proteins, they are transported through the reticulum tubules toward the portions of the smooth ER that lie nearest the Golgi apparatus Small transport vesicles, composed of small envelopes of smooth ER, continually break away and diffuse to the deepest layer of the Golgi apparatus The transport vesicles instantly fuse with the Golgi apparatus and empty their contents into the vesicular spaces of the Golgi apparatus Here, more carbohydrates are added to the secretions, and the

ER secretions are compacted As the secretions pass toward the outermost layers of the Golgi apparatus, the compaction and processing continue Finally, small and large vesicles break away from the Golgi apparatus, carrying with them the compacted secretory substances These substances can then diffuse throughout the cell

In a highly secretory cell, the vesicles formed by the

Golgi apparatus are mainly secretory vesicles, which

dif-fuse to the cell membrane, dif-fuse with it, and eventually empty their substances to the exterior via a mechanism

called exocytosis Some of the vesicles made in the Golgi

Introduction to Physiology: The Cell and General Physiology

apparatus, however, are destined for intracellular use For example, specialized portions of the Golgi appara-tus form lysosomes

Extraction of Energy From Nutrients by the Mitochondria (p 22)

The principal substances from which the cells extract energy are oxygen and one or more of the foodstuffs—carbohydrates, fats, and proteins—that react with oxy-gen In humans, almost all carbohydrates are converted

to glucose by the digestive tract and liver before they reach the cell; similarly, proteins are converted to amino

acids, and fats are converted to fatty acids Inside the cell,

these substances react chemically with oxygen under the influence of enzymes that control the rates of reaction and channel the released energy in the proper direction

Oxidative Reactions Occur Inside the Mitochondria, and Energy Released Is Used to Form ATP ATP is a nucleotide

composed of the nitrogenous base adenine, the pentose sugar ribose, and three phosphate radicals The last two

phosphate radicals are connected with the remainder of

the molecule by high-energy phosphate bonds, each of

which contains about 12,000 calories of energy per mole

of ATP under the usual conditions of the body The high-energy phosphate bonds are labile so they can be split instantly whenever energy is required to promote other cellular reactions

When ATP releases its energy, a phosphoric acid

radical is split away, and adenosine diphosphate (ADP)

is formed Energy derived from cell nutrients causes the ADP and phosphoric acid to recombine to form new ATP, with the entire process continuing over and over again

Most of the ATP Produced in the Cell Is Formed in Mitochondria After entry into the cells, glucose is subjected to enzymes in the cytoplasm that convert it

to pyruvic acid, a process called glycolysis Less than

5 percent of the ATP formed in the cell occurs via glycolysis

Pyruvic acid derived from carbohydrates, fatty acids derived from lipids, and amino acids derived from proteins are all eventually converted to the compound

acetyl–coenzyme A (acetyl-CoA) in the mitochondria

matrix This substance is then acted on by another series of enzymes in a sequence of chemical reactions

called the citric acid cycle, or Krebs cycle.

In the citric acid cycle, acetyl-CoA is split into

hydro-gen ions and carbon dioxide Hydrohydro-gen ions are highly

The Cell and Its Functions 17

reactive and eventually combine with oxygen that has diffused into the mitochondria This reaction releases a tremendous amount of energy, which is used to convert large amounts of ADP to ATP This requires large num-bers of protein enzymes that are integral parts of the mitochondria

The initial event in ATP formation is removal of an electron from the hydrogen atom, thereby converting it

to a hydrogen ion The terminal event is movement of the hydrogen ion through large globular proteins called

ATP synthetase, which protrude through the

mem-branes of the mitochondrial membranous shelves, which

themselves protrude into the mitochondrial matrix ATP synthetase is an enzyme that uses the energy and movement of the hydrogen ions to effect the conver-sion of ADP to ATP, and hydrogen ions combine with oxygen to form water The newly formed ATP is trans-ported out of the mitochondria to all parts of the cell cytoplasm and nucleoplasm, where it is used to energize the functions of the cell This overall process is called

the chemosmotic mechanism of ATP formation.

ATP Is Used for Many Cellular Functions ATP promotes

three types of cell function: (1) membrane transport,

as occurs with the sodium-potassium pump, which transports sodium out of the cell and potassium into

the cell; (2) synthesis of chemical compounds throughout

the cell; and (3) mechanical work, as occurs with the

contraction of muscle fibers or with ciliary and ameboid motion

Locomotion and Ciliary Movements of Cells (p 24)

The most obvious type of movement in the body is that

of the specialized muscle cells in skeletal, cardiac, and smooth muscle, which constitute almost 50 percent of the entire body mass Two other types of movement

occur in other cells: ameboid locomotion and ciliary

movement.

Ameboid Movement of an Entire Cell in Relation to Its Surroundings An example of ameboid locomotion is the movement of white blood cells through tissues Typically, ameboid locomotion begins with protrusion

of a pseudopodium from one end of the cell This results

from continual exocytosis, which forms a new cell membrane at the leading edge of the pseudopodium, and continual endocytosis of the membrane in the mid and rear portions of the cell

Two other effects are also essential to the forward movement of the cell The first effect is attachment

Introduction to Physiology: The Cell and General Physiology

of the pseudopodium to the surrounding tissues so it becomes fixed in its leading position while the remain-der of the cell body is pulled forward toward the point

of attachment This attachment is effected by receptor proteins that line the insides of the exocytotic vesicles.The second requirement for locomotion is avail-able energy needed to pull the cell body in the direction

of the pseudopodium In the cytoplasm of all cells are

molecules of the protein actin When these molecules

polymerize to form a filamentous network, the work contracts when it binds with another protein, for

net-example, an actin-binding protein such as myosin The

entire process, which is energized by ATP, takes place

in the pseudopodium of a moving cell, in which such

a network of actin filaments forms inside the growing pseudopodium

The most important factor that usually initiates

ame-boid movement is the process called chemotaxis, which

results from the appearance of certain chemical

sub-stances in the tissue called chemotactic subsub-stances.

Ciliary Movement Is a Whiplike Movement of Cilia on the Surfaces of Cells Ciliary movement occurs in only two places in the body: on the inside surfaces of the

respiratory airways and on the inside surfaces of the uterine tubes (i.e., the fallopian tubes of the reproductive

tract) In the nasal cavity and lower respiratory airways, the whiplike motion of the cilia causes a layer of mucus

to move toward the pharynx at a rate of about 1 cm/min;

in this way, passageways with mucus or particles that become entrapped in the mucus are continually cleared

In the uterine tubes, the cilia cause slow movement of fluid from the ostium of the uterine tube toward the uterine cavity; it is mainly this movement of fluid that transports the ovum from the ovary to the uterus.The mechanism of the ciliary movement is not fully understood, but at least two factors are necessary: (1) available ATP and (2) appropriate ionic conditions, including appropriate concentrations of magnesium and calcium

Genes in the Cell Nucleus Control Protein Synthesis (p 27)

The genes control protein synthesis in the cell and in this way control cell function Proteins play a key role

in almost all functions of the cell by serving as enzymes that catalyze the reactions of the cell and as major components of the physical structures of the cell.Each gene is a double-stranded, helical molecule of

deoxyribonucleic acid (DNA) that controls formation

of ribonucleic acid (RNA) The RNA, in turn, spreads

throughout the cells to control the formation of a

spe-cific protein The entire process, from transcription of the genetic code in the nucleus to translation of the RNA

code and formation of proteins in the cell cytoplasm,

is often referred to as gene expression and is shown in

Figure 3–1 Because there are about 30,000 genes in each cell, it is possible to form large numbers of different cel-lular proteins In fact, RNA molecules transcribed from

Cytosol

RNAsplicingRNA transport

Introduction to Physiology: The Cell and General Physiology

the same gene can be processed in different ways by the cell, giving rise to alternate versions of the protein The total number of different proteins produced by various cell types in humans is estimated to be at least 100,000

Nucleotides Are Organized to Form Two Strands of DNA Loosely Bound to Each Other Genes are attached in an end-on-end manner in long, double-stranded, helical molecules

of DNA that are composed of three basic building blocks:

(1) phosphoric acid, (2) deoxyribose (a sugar), and (3) four

nitrogenous bases: two purines (adenine and guanine) and

two pyrimidines (thymine and cytosine)

The first stage in DNA formation is the tion of one molecule of phosphoric acid, one molecule

combina-of deoxyribose, and one combina-of four bases to form a

nucleo-tide Four nucleotides can therefore be formed, one

from each of the four bases Multiple nucleotides are bound together to form two strands of DNA, and the two strands are loosely bound to each other

The backbone of each DNA strand is composed of alternating phosphoric acid and deoxyribose molecules The purine and pyrimidine bases are attached to the side

of the deoxyribose molecules, and loose bonds between the purine and pyrimidine bases of the two DNA strands

hold them together The purine base adenine of one strand

always bonds with the pyrimidine base thymine of the other strand, whereas guanine always bonds with cytosine.

The Genetic Code Consists of Triplets of Bases Each group of three successive bases in the DNA strand

is called a code word These code words control the

sequence of amino acids in the protein to be formed

in the cytoplasm One code word, for example, might

be composed of a sequence of adenine, thymine, and guanine, whereas the next code word might have a sequence of cytosine, guanine, and thymine These two code words have entirely different meanings because their bases are different The sequence of successive code

words of the DNA strand is known as the genetic code.

THE DNA CODE IN THE NUCLEUS IS TRANSFERRED

TO RNA CODE IN THE CELL CYTOPLASM—THE PROCESS OF TRANSCRIPTION (p 30)

Because DNA is located in the nucleus and many tions of the cell are carried out in the cytoplasm, there must be some method by which the genes of the nucleus control the chemical reactions of the cytoplasm This is achieved through RNA, the formation of which is con-trolled by DNA During this process the code of DNA

func-is transferred to RNA, a process called transcription

Genetic Control of Protein Synthesis, Cell Function, and Cell

Reproduction 21

The RNA diffuses from the nucleus to the nuclear pores into the cytoplasm, where it controls protein synthesis

RNA Is Synthesized in the Nucleus From a DNA Template

During synthesis of RNA, the two strands of the DNA molecule separate, and one of the two strands is used as

a template for RNA synthesis The code triplets in DNA

cause the formation of complementary code triplets (called

codons) in RNA; these codons then control the sequence

of amino acids in a protein to be synthesized later in the cytoplasm Each DNA strand in each chromosome carries the code for perhaps as many as 2000 to 4000 genes.The basic building blocks of RNA are almost the same as those of DNA except that in RNA, the sugar

ribose replaces the sugar deoxyribose and the

pyrimi-dine uracil replaces thymine The basic building blocks

of RNA combine to form four nucleotides, exactly as described for the synthesis of DNA These nucleotides

contain the bases adenine, guanine, cytosine, and uracil The next step in the RNA synthesis is activation of

the nucleotides, which occurs through the addition of

two phosphate radicals to each nucleotide to form phosphates These last two phosphates are combined

tri-with the nucleotide by high-energy phosphate bonds,

which are derived from the adenosine triphosphate (ATP) of the cell This activation process makes avail-able large quantities of energy, which is used for pro-moting the chemical reactions that add each new RNA nucleotide to the end of the RNA chain

The DNA Strand Is Used as a Template to Assemble the RNA Molecule From Activated Nucleotides The assembly

of the RNA molecule occurs under the influence of the

enzyme RNA polymerase as follows:

1 In the DNA strand immediately ahead of the gene that is to be transcribed is a sequence of nucleotides

called the promoter An RNA polymerase recognizes

this promoter and attaches to it

2 The polymerase causes unwinding of two turns of the DNA helix and separation of the unwound portions

3 The polymerase moves along the DNA strand and begins forming the RNA molecules by binding com-plementary RNA nucleotides to the DNA strand

4 The successive RNA nucleotides then bind to each other to form an RNA strand

5 When the RNA polymerase reaches the end of the DNA gene, it encounters a sequence of DNA mole-

cules called the chain-terminating sequence,

caus-ing the polymerase to break away from the DNA strand The RNA strand is then released into the nucleoplasm

Introduction to Physiology: The Cell and General Physiology

The code present in the DNA strand is transmitted

in complementary form to the RNA molecule as lows:

1 Precursor messenger RNA (pre-mRNA), a large,

im-mature single strand of RNA that is processed in the nucleus to form mature mRNA and includes two different types of segments called introns, which are removed by a process called splicing, and exons, which are retained in the final mRNA

2 Small nuclear RNA (snRNA), which directs the

splicing of pre-mRNA to form mRNA

3 mRNA, which carries the genetic code to the

cyto-plasm to control the formation of proteins

4 ribosomal RNA, which, along with proteins, forms

the ribosomes, the structures in which protein ecules are assembled

5 Transfer RNA (tRNA), which transports activated

amino acids to the ribosomes to be used in the sembly of the proteins

6 microRNA (miRNA), which are single-stranded

RNA molecules of 21 to 23 nucleotides that can regulate gene transcription and translation

There are 20 types of tRNA, each of which combines specifically with one of the 20 amino acids and carries this amino acid to the ribosomes, where it is incorporated

in the protein molecule The code in the tRNA that allows

it to recognize a specific codon is a triplet of nucleotide

bases called an anticodon During formation of the

pro-tein molecule, the three anticodon bases combine loosely

by hydrogen bonding with the codon bases of the mRNA

In this way, the various amino acids are lined up along the mRNA chain, thus establishing the proper sequence of amino acids in the protein molecule